Photovoltages

Besides improving stability, a practical goal of surface modification has been to utilize redox reactions, otherwise not applicable, to yield better electrical characteristics such as higher open-circuit photovoltage, and to promote high conversion efficiencies. 

Differences in behavior between polycrystalline and single-crystal CdSe electrodes in polysulfide PEC involving the short- and long-term changes in photovoltage and photocurrents have been discussed by Cahen et al. [88], on the basis of XPS studies, which verified the occurrence of S/Se substitution in these electrodes when immersed in polysulfide solution, especially under illumination. The presence of a thin (several nanometers) layer of CdS on top of the CdSe was shown to influence... 

The prototype DSCs used liquid electrolytes, typically L/I2 in an organic solvent such as propylene carbonate. The electron generation/collection problem in this cell has been discussed analytically with the help of intensity-modulated photocurrent and photovoltage spectroscopy [314]. A particularly challenging issue has been the replacement of the liquid electrolyte with a solid charge-transport material... 

Mandal KC (1990) Fermi level shift with photovoltages at zinc modified CdSe surfaces. J Mater Sci Lett 9 1203-1204... 

Roy AM, De GC, Sasmal N, Bhattacharyya SS (1995) Determination of the flatband potential of semiconductor particles in suspension by photovoltage measurement. J Hydrogen Energy 20 627-630... 

The photovoltage is esentially determined by the ratio of the photo- and saturation current. Since io oomrs as a pre-exponential factor in Eq. 1 it determines also the dark current. Actually this is the main reason that it limits the photovoltage via Eq. 2, The value of io depends on the mechanism of charge transfer at the interface under forward bias and is normally different for a pn-junction and a metal-semiconductor contact. In the first case electrons are injected into the p-region and holes into the n-region. These minority carriers recombine somewhere in the bulk as illustrated in Fig. 1 c. In such a minority carrier device the forward current is essentially determined... 

Similarly as in solid state devices the photovoltage Uph is the given by (i = 0) ... 

Table 1. Photovoltage Up, photocurrent ip fill factor FF and efficiency p of regenerative electrochemical solar cells... 

In this case, however, the standard potential is very negative resulting in a very small photovoltage. In this respect single crystals of layer-compounds are favorable materials because of their special surface morphology. 

A p-i-n diode has been used on glass and on polyimid as a position-sensitive detector [638, 639]. The position of an incident light spot is measured by means of the lateral photovoltage. 

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